Implement D&D 5e death-save state machine and cleanup combat ordering

- Add status-driven death-save model:
  - status: conscious | dying | stable | dead
  - deathSaveSuccesses/deathSaveFailures as display counters
  - remove old death-save fields as source of truth
- Add death-save actions:
  - success, fail, nat1, nat20
  - stabilize participant
  - revive dead participant to 0 HP, stable, unconscious
- Apply 5e HP transition rules:
  - characters and NPCs at 0 HP become dying
  - stable/dying participants gain unconscious condition
  - healing clears death saves and returns conscious
  - massive damage kills
  - non-NPC monsters at 0 HP become dead and inactive
- Split NPCs from monsters with type="npc":
  - NPCs use death saves like characters
  - NPCs remain DM-controlled/monster-colored in UI
  - new NPCs no longer persist isNpc flag
- Keep dead PCs/NPCs in encounter and initiative until DM removes or deactivates
- Allow DM active/inactive toggle for dead participants
- Hide inactive participants from player display
- Improve DM and player death-state UI:
  - show Dying/Dead/Unconscious states consistently
  - add revive button for dead participants
  - distinguish dead visual from inactive visual in DM view
- Fix initiative drag/reorder behavior:
  - downward drag now changes order instead of no-op
  - paused combat can reorder across current turn pointer
  - turnOrderIds stay synced to participants order
- Persist campaign collapse state in localStorage
- Update death-save docs and encounter builder docs
- Add/expand tests for:
  - death saves and HP transitions
  - dead/active/inactive behavior
  - NPC death-save behavior
  - player display visibility
  - drag reorder semantics
  - logging expectations

Tests:
- npm run test:all
- app: 94 passed
- shared: 158 passed, 5 skipped
- server: 32 passed

shared/tests/turn.combat.test.js

@@ -56,7 +56,7 @@ function setupEncounter() {
     buildMonsterParticipant({ name:'Goblin2', maxHp:100, initMod:2 }).participant,
     buildMonsterParticipant({ name:'OrcBoss', maxHp:500, initMod:1 }).participant,
     buildMonsterParticipant({ name:'Wolf', maxHp:120, initMod:3 }).participant,
-    buildMonsterParticipant({ name:'Merchant', maxHp:150, initMod:0, isNpc:true }).participant,
+    buildMonsterParticipant({ name:'Merchant', maxHp:150, initMod:0, asNpc:true }).participant,
   ];
   // give deterministic ids to monsters for assertions
   const idMap = { Goblin1:'m1', Goblin2:'m2', OrcBoss:'m3', Wolf:'m4', Merchant:'n1' };
@@ -163,12 +163,12 @@ describe('combat integrity (100 rounds, full op coverage)', () => {
           }
         }
         // 5. deathSave
-        if (actor && actor.currentHp <= 0 && !actor.isNpc) {
-          try { const r = await deathSave(e, actor.id, 'fail', 1, ctx); e = r.enc; } catch (err) {}
+        if (actor && actor.status === 'dying' && actor.type !== 'npc') {
+          try { const r = await deathSave(e, actor.id, 'fail', ctx); e = r.enc; } catch (err) {}
         }
-        // 6. removeParticipant
+        // 6. removeParticipant (monsters/NPC only; dead PCs stay until DM removes manually)
         if (totalTurns % 5 === 0) {
-          const dead = e.participants.find(part => (part.isDying || part.currentHp <= 0) && (part.isNpc || part.name.startsWith('Goblin') || part.name === 'OrcBoss' || part.name === 'Wolf'));
+          const dead = e.participants.find(part => (part.status === 'dead' || part.currentHp <= 0) && (part.type === 'npc' || part.name.startsWith('Goblin') || part.name === 'OrcBoss' || part.name === 'Wolf'));
           if (dead) { try { e = await removeParticipant(e, dead.id, ctx); } catch (err) {} }
         }
         // 7. addParticipant